Fuel injection amounts are typically set based on a desired air/fuel ratio and adapted using feedback from one or more exhaust gas sensors in the exhaust. Fueling errors may occur, however, during operating conditions where fuel vapors are present in the intake. For example, fuel vapor canisters designed to trap fuel vapors from the fuel tank are periodically purged to the intake, and these vapors may result in an excess amount of fuel in the cylinders, wasting fuel and degrading emissions.
Previous solutions to account for the amount of fuel originating from the fuel vapor canister have relied on purge flow estimates, based on purge duration and other parameters. However, these estimates are frequently inaccurate. Further, these estimates don't take into account additional sources of intake fuel, such as fuel from the positive crankcase ventilation system or pushback fuel.
The inventors have recognized the issues with the above approach and offer a method to at least partly address them. In one embodiment, a method comprises adjusting fuel injection based on fuel concentration in an engine intake manifold, and during idle and when EGR is disabled, adjusting fuel injection based on the fuel concentration and a fuel pushback amount. In this way, fuel injection may be adjusted based on fuel vapors present in the intake, for example, from both a fuel vapor canister purge and from a positive crankcase ventilation system. In one example, these fuel vapor amounts may be determined based on an oxygen sensor present in the intake. Further, the fuel injection may be additionally adjusted based on an amount of pushback fuel, for example from fuel evaporated from a fuel puddle on an intake valve or port.
By determining the amount of fuel in the intake based on a signal from an oxygen sensor, fuel injection amounts may be adjusted to maintain desired air/fuel ratio in the cylinder. Depending on operating conditions, the intake oxygen concentration may be able to provide an indication of an amount of ambient humidity, fuel vapors from various sources, and/or an amount of exhaust gas recirculation in the intake. By determining these amounts in some conditions and modeling them in other conditions, optimal air/fuel ratio may be maintained, improving fuel economy and reducing emissions. Further, the amount of vapors can also be adjusted based on feedback from exhaust air-fuel ratio sensors, purge flow estimates, purge duration, and other parameters if desired.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.